1. Field of the Invention
The present invention relates to a technique for removing a foreign substance adhered to an optical member of an image capturing apparatus such as a video camera or a digital still camera.
2. Description of the Related Art
In recent years, as the resolution of an optical sensor in an image capturing apparatus improves, dirt (foreign substance) which adheres to an optical system in use, adversely influences the captured image has become problematic. The resolutions of especially image capturing elements built in a video camera and a still camera are remarkably improving. For this reason, when external dust or a foreign substance such as abrasion powder produced by an internal mechanical sliding surface adheres to, for example, an infrared cutoff filter or an optical low-pass filter placed near an image capturing element, the following phenomenon often occurs. That is, the captured image may contain the foreign substance because the image capturing element has high resolution and an image on its surface blurs little.
When dust adheres to a member in an image capturing apparatus, the image quality is recovered as the user wipes away it. However, the user has no choice but to confirm dust, which has adhered to the apparatus in use, after image capturing. The image captured while dust adheres to the apparatus contains an image of the dust and therefore must be corrected using software.
Under the circumstance, a camera including a dust proof mechanism that exploits vibration has been commercialized. The dust proof mechanism that exploits vibration requires a considerable amount of vibration energy. To meet this requirement, Japanese Patent Laid-Open No. 2007-267189 discloses the following technique. A support member is positioned between a node of vibration in at least one vibration mode and that of vibration in another vibration mode, which have an interval between them, that is narrower than that between other two nodes, and a plurality of vibration modes are simultaneously generated in an optical member by an electromechanical energy conversion element. This removes dust adhering on the optical member while suppressing loss of vibration energy and reducing the energy consumption of a dust removing apparatus, and suppresses deterioration in optical characteristic due to heat generation.
A method of simultaneously generating a plurality of vibration modes, as disclosed in Japanese Patent Laid-Open No. 2007-267189, will be described with reference to a view of the arrangement of a dust removing apparatus built in a digital still camera, as shown in FIG. 7.
Referring to FIG. 7, a digital still camera includes an image capturing element package 14 including an image capturing element portion 14-1 and cover glass 14-2, and a dust removing apparatus. The dust removing apparatus includes piezoelectric elements, 2-1 and 2-2 which serve as vibrating bodies, a support member 61, a driving circuit 13, and an optical filter 51.
However, to generate a plurality of vibration modes, the conventional dust removing mechanism needs to drive piezoelectric elements serving as a plurality of electromechanical energy conversion elements at a plurality of driving frequencies. Hence, a plurality of driving circuits with different output frequencies are necessary. When a piezoelectric element is arranged on the optical filter 51, it needs to fall outside the image capturing region. Also, when a plurality of piezoelectric elements are used, the necessary area of an expensive optical filter increases. Furthermore, an increase in size of an optical filter often hinders downsizing of a camera.